Electrical cable having crosslinked insulation with internal pulling lubricant

ABSTRACT

Electrical power cable having a reduced surface coefficient of friction and required installation pulling force, and the method of manufacture thereof, in which the central conductor core, with or without a separate insulating layer, is surrounded by a sheath of crosslinked polyethylene. A high viscosity, high molecular weight silicone based pulling lubricant or fatty acid amide pulling lubricant is incorporated by alternate methods with the polyethylene to form a composition from which the outer sheath is extruded, and is effective to reduce the required pulling force on the cable during installation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.14/666,105, filed Mar. 23, 2015, which is a continuation of U.S.application Ser. No. 12/406,454, filed Mar. 18, 2009 and now issued asU.S. Pat. No. 8,986,586, all of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to electrical power cables havingcrosslinked insulation, more particularly to methods for reducing theinstallation pulling force of electrical cables having crosslinkedinsulation, and even more particularly to preferred pulling lubricantcompositions for effecting such reduction.

BACKGROUND OF THE INVENTION

Electrical power cables typically include a conductor core and an outerjacket or sheath. The “conductor core”, as used herein and throughoutthe specification and claims, may be, for example, a single metal wire,multiple small wires twisted together to make a “stranded” cable,multiple insulated wires, or other types of electrical conductors actingtogether to serve a particular power function (e.g., three-phaseconnection). The term “sheath,” as used herein and throughout thespecification and claims, means the outermost covering surrounding theconductor core, whether of a single type material or multiple layers ofthe same or different material. The sheath may comprise one or morelayers of polymeric or other material to provide physical, mechanical,electrical insulating and/or chemical protection for the underlyingcable components. Crosslinked polymers such as crosslinked polyethylene(XLPE) are used as electrical insulation layers or jackets for variouselectrical power cable types such as type XHHW, type RHH/RHW, and typeUSE cables

Installation of electrical power cable often requires that it be pulledthrough tight spaces or small openings in, and in engagement with,narrow conduits, raceways, cabletrays, or passageways in rafters orjoists. This becomes problematic since the exterior surface of the cablesheath normally has a multitude of forces acting on it, thereforerequiring a large pulling force. Moreover, installation parametersinclude maximum allowable cable pulling tension and/or sidewall pressurelimits. Exceeding these limits can result in degradation of the cable,physical damage and inferior installation.

To overcome this problem, the general industry practice has been to coatthe exterior surface of the cable sheath with a lubricant at the jobsite in order to reduce the coefficient of friction between this surfaceand the conduit walls or like surfaces, typically using vaselines orlubricants produced specifically for such purpose, such as Yellow 77®(hereinafter, “Y 77”). However, applying a lubricant like Y 77 to thefinished cable at the job site poses problems, principally theadditional time, expense and manpower required to lubricate the finishedcable surface at the job site as well as to clean up after thelubricating process is completed.

Alternative solutions have been proposed, including the application of aseparate lubricant layer after the polymeric sheath has been formed orextruded during the manufacturing of the cable, or the application ofgranules of material to the still-hot sheath during the extrusionprocess, which granules are designed to become detached when the cableis pulled through the duct. These solutions not only require majoralterations of the manufacturing line, but result in a loss inmanufacturing time, increased economic costs, and undesirablefluctuations in the geometrical dimensions of the cable sheaths. Otherproposed solutions have involved spraying, dipping, or otherwiseexternally applying a “pulling” lubricant to the exterior surface of thesheath, but these techniques have not been satisfactory for allconditions of service.

As a result, a major breakthrough in this area has been the developmentof an innovative process by which a preselected pulling lubricant, ofappropriate type and sufficiency, is internally introduced during thecable manufacture into the material that is to form the sheath, so thatthe pulling lubricant, either by migration through, or permeationthroughout, the sheath becomes available at the exterior surface of thecable sheath at the time of the cable's installation, and is effectiveto reduce the amount of force required to install the cable. Thisprocess is described in U.S. Pat. No. 7,411,129, assigned to theassignee of the present invention, and is incorporated herein byreference in its entirety. The hereindescribed invention is a specificimprovement to such process, as applied to crosslinked insulation of thesheath.

It is important to an understanding of the present invention to know thedifference between what are referred to as “pulling lubricants” and whatare “processing lubricants.” A pulling lubricant is a lubricant thatappears at the outside surface of the sheath of the cable and iseffective to reduce the force necessary to install the cable throughbuilding conduits and the like. A processing lubricant is lubricatingmaterial that is used to facilitate the cable manufacturing process,such as improving the flow of polymer chains during any polymercompounding as well as during the extrusion processes while the polymeris in its molten or melt phase. Cable manufacturers have long usedprocessing lubricants, such as stearic acid or ethylene bis-stearamidewax, as a minor component of the polymeric compound from which the cablesheath is formed. Because a processing lubricant is normally noteffective except when the polymer is in this melt phase, the effect of aprocessing lubricant as an external lubricant is essentiallynon-existent in the final hardened polymer sheath of the cable. Evenwhere there may be an excessive amount of the processing lubricant, aseparate pulling lubricant would still be required to sufficientlyreduce the cable sheaths' exterior surface coefficient of friction aswell as minimize the pulling force necessary to install the cable.

Accordingly, there has been a long-felt need for an effective method ofproviding a pulling lubricant at the exterior surface of finished powercables having insulation formed of crosslinked polymeric material, inwhich the pulling lubricant is effective to reduce the requiredinstallation pulling force.

SUMMARY OF THE INVENTION

As a consequence, this invention is directed to the use of certainpulling lubricants in electrical cable sheaths containing crosslinkedpolymers such as polyethylene. One embodiment of the invention providesa crosslinkable silane-ethylene copolymer impregnated with an effectiveamount of pulling lubricant, wherein the pulling lubricant does notdeleteriously interfere with the subsequent crosslinking of the basepolymer, and in the finished electrical cable, the pulling lubricant isavailable at the surface of the outer sheath of the electrical cable toreduce the cable sheath's exterior surface coefficient of friction andreduce the pulling force necessary to install the cable at the time ofthe cable's installation. The pulling lubricant generally is a highviscosity silicone, preferably polydimethylsiloxane, or a fatty acidamide such as erucamide or oleamide, and is present in an amount in therange of from about 2 to about 15% by weight, based on the total weightof the outer sheath.

In another embodiment, a method of forming a crosslinked polyethylenesheath for an electrical cable is provided, such method including (1)blending a crosslinkable polyethylene resin or ethylene copolymer with asilicone or fatty acid amide to form a blend, (2) processing the blendinto a shape of a sheath for an electrical cable and (3) crosslinkingthe blend to form the crosslinked polyethylene sheath. The silicone orfatty acid amide is present in an amount in the range of from about 2 toabout 15 weight percent, based on the total weight of the crosslinkedpolyethylene sheath.

As described in more detail below, the methods of this invention includeintroducing a pulling lubricant, of optimum weight percentage orquantity, into the manufacturing process at a particular stage ofmanufacture, which results in the pulling lubricant being present in theouter sheath, so that it is available to reduce the cable sheaths'exterior surface coefficient of friction and to minimize the pullingforce necessary to install the cable. In theory, this is as aconsequence of the migration of the pulling lubricant to the sheathsurface; or alternatively, due to the permeation of the pullinglubricant throughout the sheath, depending upon the particularcompositions.

As described in detail below, a crosslinked polyethylene sheath of afinished power cable is produced by the described method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other details and aspects of the invention, as well as theadvantages thereof, will be more readily understood and appreciated bythose skilled in the art from the following detailed description, takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of typical equipment used in themanufacture of cable in accordance with the present invention, whenmixing the pulling lubricant with the crosslinkable polyethylenematerial prior to extrusion;

FIG. 2 is a representation of a test device which may be used indetermining the coefficient of friction and related installation pullingforces of electrical cables of the present invention;

FIG. 3 is a graphical representation of test data obtained from the testdevice in FIG. 2 which compares the coefficient of friction of differentXHHW cables incorporating varying amounts of pulling lubricant; and

FIGS. 4-7 are graphical representations of test data obtained from alarge scale test device and which compare the required pulling force ofdifferent XHHW cables incorporating varying amounts of pullinglubricant.

FIGS. 8A-8B are schematic illustrations of a cable comprising aplurality of sheath layers.

DETAILED DESCRIPTION OF THE INVENTION Composition

Polymeric materials used in compositions of the present inventioninclude polyethylene, polypropylene, polyvinylchloride, organicpolymeric thermosetting and thermoplastic resins and elastomers,polyolefins, copolymers, vinyls, olefin-vinyl copolymers, polyamides,acrylics, polyesters, fluorocarbons, and the like. Polyethylene resinsuseful in the present invention may include low density polyethylene,linear low density polyethylene, high density polyethylene,silane-grafted polyethylene, ethylene copolymers and combinationsthereof. As previously described, for cables of the present invention,the conductor core of a single solid or stranded conductor is preferablysurrounded by an insulating layer of low density crosslinkedpolyethylene (XLPE).

Crosslinked polyethylene (XLPE) may be produced by any method known inthe art and preferably includes incorporating alkoxysilane functionalityinto the polymer structure either by grafting unsaturated alkoxysilanesonto the ethylene polymers or by direct copolymerization of ethylenewith unsaturated alkoxysilanes. The silane-ethylene copolymer can becrosslinked, for example, by exposing the copolymer to moisture or steamin the presence of an organometallic catalyst, e.g.,dibutyl-tin-dilaurate. Polyethylene resins useful in the presentinvention are capable of being crosslinked by a reactive unsaturatedsilane compound and exposure to water. Polyethylene crosslinkingcompounding materials are available from a number of manufacturers whichsupply silane pre-grafted base resins (the silane compound(s) beinggrafted onto the polyethylene resin by reactive extrusion) and catalystmasterbatches that can be mixed in proper proportions. For example,crosslinkable polyethylene system components are available fromPadanaplast USA under the trade designation “Pexidan®” (includingPexidan® V/T, Pexidan® X/T, Pexidan® U/T, Pexidan® R/T, Pexidan® H/T andPexidan® L/T) that include a silane pregraft (designated A-3001) and acatalyst masterbatch such as, for example, CAT-010FR, CAT-005FR,CAT-008, CAT-009, CAT-012FR, CAT-003, and CAT-047FRUV.

Alternatively, polyethylene crosslinkable compounds useful in thepresent invention (which may or may not be grafted or copolymerized withsilane) are combined with a suitable crosslinking agent such as aheat-activated organic peroxide. The crosslinkable compounds may then becrosslinked by heat (and to a lesser extent, pressure) such as forexample by steam curing. Other forms of curing also may be employed suchas for example by using heated pressurized gasses such as nitrogen.

Generally, the crosslinkable polyethylene polymers are present incompositions of the present invention in an amount in the range of fromabout 20 to about 99 weight percent, based on the total weight of thecomposition, preferably in the range of from about 30 to about 85 weightpercent based on the total weight of the composition, and morepreferably in an amount in the range of from about 40 to about 80 weightpercent, based on the total weight of the composition.

Compositions of the present invention further include a pullinglubricant in an amount sufficient to reduce the coefficient of frictionof the exterior surface of the sheath/cable and reduce the requiredcable pulling force during the cable's installation. Useful pullinglubricants include high viscosity silicones such as, for example,polydimethylsiloxane. The preferred pulling lubricant ispolydimethylsiloxane or a fatty acid amide such as erucamide or oleamidein an amount in the range of from about 2 to about 15 weight percentbased on the total weight of the composition.

When incorporated into a finished electrical cable sheath, the pullinglubricant is continuously available at the surface of the sheath/cableupon installation as a consequence of the migration of the pullinglubricant to the sheath surface during installation; or alternatively,due to the permeation of the pulling lubricant throughout the sheath.Under these circumstances, the pulling lubricant is effective to reducethe installation pulling force of the electrical cable.

Compositions of the present invention may further comprise additivesknown in the art, such as for example, flame retardants/catalysts andcolor concentrates.

Preparation of Compositions

Referring initially to FIG. 1, there is depicted typical equipment 11for manufacturing electrical cable 12 in accordance with one process ofthe present invention. The outer sheath of the cable is of an extrudedcrosslinked polymeric material such as polyethylene. The equipment 11may include a reel 13 which supplies conductor wire 14 to an extrudinghead 15. In flow communication with the extrusion head is a tank 16 ofcrosslinkable polyethylene pellets 17. A tank 18 with the desiredpulling lubricant 19 is adapted to be in flow communication with thetank 16 by way of conduit 22, thus enabling the mixing of the pullinglubricant with the pellets 17, the mixture thereafter introduced intothe extruder. Alternatively, the tank may be adapted to be in fluidcommunication with the extruder or extrusion head 15, by way of conduit23, downstream from the point of entry of the polyethylene material,thus allowing the pulling lubricant to mix with the polyethylene whilein its molten state in the extruder or extruder head. A cooling box 20for cooling the extruded product is provided, and a reel 21 ispositioned for taking up the resulting cable assembly 12. When the finalcable construction is such that there are multiple layers of sheathmaterial (such as the electrical cable 30 comprising conductor wire 31,inner sheath layer 32 and outer sheath layer 33, as shown in FIGS.8A-8B), the pulling lubricant should desirably be incorporated into theoutermost layer (e.g., outer sheath layer 33, as shown in FIGS. 8A-8B).

As is therefore evident, the pulling lubricant can be mixed with thematerial from which the outer sheath is to be extruded prior toextrusion or, alternatively, introduced into the extruding head forsubsequent mixing with the molten extrusion material as the sheath isbeing formed. As a further alternative, the pulling lubricant can beinitially compounded with the polymeric material of the pelletsthemselves in a process upstream of that depicted in FIG. 1, therebyforming lubricated polymeric pellets, thus eliminating the need for tank18 and conduits 22 and 23.

Preferably, the pulling lubricant is incorporated into a crosslinkablepolyethylene copolymer by using a masterbatch system, thereby forming acarrier for the pulling lubricant. By using a masterbatch, highconcentrations of the pulling lubricant are formulated with thecrosslinkable polyethylene system in such quantities as to produce anappropriate concentration of the pulling lubricant in the final mixture.Where a masterbatch is used, the concentration of pulling lubricantgenerally is in the range of up to about 25%, but may be higher. Aliquotparts of the masterbatch mixture may then be added to the resin systemand other components in various percentages permitting a relativelyuniform dispersion of the pulling lubricant in the product atappropriate levels. For example, a 25% masterbatch of pulling lubricantadded as 5% of the total mixture results in a final lubricantconcentration of 1.25%, and a 25% masterbatch of pulling lubricant addedas 10% of the total mixture results in a final lubricant concentrationof 2.5%, etc. Generally, the amount of pulling lubricant contained inthe final compound mixture is in the range of from about 2 to about 15%based on the total weight of the composition.

To adjust the levels of pulling lubricant in the final mixture, a secondpolymeric material may be included in the mixture formulation. Thesecond polymeric material can be the same or different as the polymericmaterial used as the polymer carrying the pulling lubricant. Preferably,the second polymeric material comprises a crosslinkable silane-ethylenecopolymer or pre-grafted polyethylene resin. Generally, the amount ofsecond polymeric material is in the range of from about 18 to about 80weight percent, based on the total weight of the composition. Flameretardants, catalysts, color concentrates and other additives may alsobe used. If such components are used, they may be kept separate from thepolymer components until the time of extrusion.

Compositions of the present invention may be prepared by kneading andblending the various components in conventional kneaders, mixers,extruders, or other commonly used compounding machines, such as asingle- or twin-screw compounding extruder, Buss kneader, Banbury mixer,two-roll mill, or other heated shear-type mixers. The melted, continuoushomogeneous matrix of resin, pulling lubricant, and optional othercomponents are then extruded to form jackets or sheaths for use inelectrical cables. In either single-layer, co-extrusion or tandemextrusion methods, a conductor, either solid or stranded, is firstintroduced into an extrusion head where the heated, melted sheathcomposition is introduced and applied to the circumference of theconductor in one or more layers. The total thickness of the coating willvary mainly depending on the dimensions of the conductor and compliancewith appropriate industry standards. The final product is thenintroduced into a cooling water bath and ultimately the cooled productis wound onto reels.

Preferably, the crosslinking of the polymers takes place subsequent tothe extrusion step. The crosslinking process may take place in air or ina sauna, or alternatively in steam or in an inert atmosphere. When usinga heat-cure method for crosslinking, the final product upon leaving theextruder head proceeds directly into a heated, pressurized chamber (ortube) where the crosslinking takes place. Generally, the chamber or tubeis at a temperature considerably higher than the extruder or headthemselves. Given the reactive nature of the polymeric components andcrosslinking agents, it was surprising to find that the finished cablesproduced with compositions of the present invention yielded a pullinglubricant continuously available at the surface of the outer sheath sothat it is available to reduce the cable sheaths' exterior surfacecoefficient of friction in order to minimize the pulling force necessaryto install the cable. Given the reactive nature of the components, itwas expected that the pulling lubricant would interfere with thecrosslinking process or react and crosslink itself, making it lessavailable at the surface of the cable sheath for lubrication.

In accordance with the testing subsequently described, it has beendetermined that, for type XHHW, type RHH/RHW, and type USE cablesspecifically, high viscosity silicones, specificallypolydimethylsiloxane, or a fatty acid amide such as erucamide oroleamide are preferred pulling lubricants to be incorporated in thecrosslinked polyethylene sheath.

EXAMPLES

The following examples are presented to further illustrate the presentinvention and are not to be construed as limiting the invention.

Example I

Various cable sheath compositions were formulated in accordance with thepresent invention for testing as described in more detail below. Asshown in Table I, a polymeric resin of crosslinkable silane-ethylenecopolymer (commercially available from Dow Chemical Company under thetrade designation Si-Link™ AC DFDB-5451 NT) was initially blended with a25% concentration of high viscosity silicone (polydimethylsiloxane) toyield a carrier-impregnated resin containing various percentages ofpulling lubricant in the final mixture as indicated in Table I. Withrespect to all samples (except V-Y), the carrier-impregnated resin wascoextruded with a pre-grafted polyethylene resin (commercially availablefrom Padanaplast USA, Inc. under the trade designation A-3001) as wellas a flame retardant/catalyst (commercially available from PadanaplastUSA, Inc. as CATOO5FR, a mixture comprising polyethylene blended with aflame retardant and a catalyst), and a color concentrate (commerciallyavailable from Dow Chemical Company under the trade designationDFNC-0039 BK). The various sheathed samples were then cooled in a waterbath prior to testing. A “control” cable was also prepared as indicatedin Table I (which did not contain any pulling lubricant in the outersheath).

TABLE I Silane-ethylene Standard copolymer pre-grafted Flame % Pullingimpregnated with polyethylene Retardant/ Sample Lubricant pullinglubricant resin Catalyst Color A 1 4 74.5 20 1.5 B 2 8 70.5 20 1.5 C 312 66.5 20 1.5 D 4 16 62.5 20 1.5 E 5 20 58.5 20 1.5 F 6 24 54.5 20 1.5G 7 28 50.5 20 1.5 H 8 32 46.5 20 1.5 I 9 36 42.5 20 1.5 J 9.5 38 40.520 1.5 K 10 40 38.5 20 1.5 L 10.5 42 36.5 20 1.5 M 11 44 34.5 20 1.5 N11.5 46 32.5 20 1.5 O 12 48 30.5 20 1.5 P 12.5 50 28.5 20 1.5 Q 13 5226.5 20 1.5 R 13.5 54 24.5 20 1.5 S 14 56 22.5 20 1.5 T 14.5 58 20.5 201.5 U 15 60 18.5 20 1.5 V+ 1 4 74.5 20 1.5 W+ 2 8 70.5 20 1.5 X+ 3 1266.5 20 1.5 Y+ 4 16 62.5 20 1.5 Control 0 0 78.5 20 1.5 * Amounts areweight percent, based on the total weight of the crosslinkedpolyethylene sheath. +Ethylene copolymer only.

Example II Coefficient of Friction Test

Referring now to FIG. 2, diagrammatically illustrated is the apparatusused to determine coefficient of friction for a given cable being pulledin conduit. The coefficient of friction test apparatus was developed togive a consistent way to determine the input values necessary to use theindustry-standard program published by PolyWater Corporation tocalculate a real-world coefficient of friction for a given cable beingpulled in conduit. Given the inputs for the conduit setup, the backtension on the wire, and the pulling tension on the pulling rope, thisprogram back-calculated a coefficient of friction for the cable bysubtracting the back tension from the pulling tension and attributingthe remaining tension on the rope to frictional forces between the cableand the conduit.

As shown in FIG. 2, the overall setup used a pulling rope threadedthrough—40′ of PVC conduit (appropriately sized for the cable beingpulled) with two 90° bends, the pulling rope threaded through a loadcell so that pulling force could be constantly monitored and logged.Attached to the pulling rope was a 100′ piece of XHHW cable to be testedcomprising three AWG 4/0 wires. The end of the XHHW test sample wasattached to a metal cable which was wrapped around a cylinder with anair brake to allow the constant back tension on the set up. The metalcable providing back-tension was also threaded through a load cell sothat it could be monitored in real-time, and continuously logged. Valuesfor both back tension and pulling tension were logged for the time ittook to pull cable through the conduit run. The resulting values werethen averaged and used in the PolyWater program to calculate coefficientof friction.

Referring now to FIG. 3, graphically illustrated is a comparison of theresulting coefficient of friction for various cable samples (made usingthe formulations described above in Example I) containing variouspercentages of pulling lubricant. As shown in FIG. 3, the linecorresponding to “Poly (yellow 77)” represents the “Control” samplecontaining standard Padanaplast crosslinked polyethylene in the exteriorsheath (with no internal pulling lubricant) which was coated with Yellow77 pulling lubricant on the exterior of the sheath for the coefficientof friction test. The line corresponding to “Poly (Dow)” corresponds toSamples V-Y (in which the additional polymer was a silane-ethylenecopolymer rather than a pre-grafted resin). The results in FIG. 3illustrate that sheaths prepared in accordance with the inventioncontaining pulling lubricant in an amount in the range of from about 2to about 15 weight percent based on the total weight of the compositionreduces the coefficient of friction of the exterior surface of the cablemore significantly than cables prepared without pulling lubricant.

Large Scale Tests

Various test cable samples (750 kcmil Aluminum XHHW, 500 kcmil CopperXHHW, and AWG 4/0 Copper XHHW) were prepared using the formulations ofSample I and the “Control” sample of Example I. The samples weresubjected to a “large scale” test to simulate “real world” installationconditions. In this test, multiple individual XHHW wires were providedon payoffs and attached to a pulling rope that was threaded through anarrangement of 3″ conduit that included a total of about 450 feet ofconduit interspersed with a total of eight 90° bends. A pulling rope wasattached to the conductors and a tugger was used to pull the cablearrangement through the conduit. The rope was threaded through a pulleyarrangement that used a load cell to monitor rope tension while the wirewas pulled through the conduit. This tension was continuously logged andaveraged to give an average pulling force for the pull. This forcecorrelated directly to the coefficient of friction for the cable. 4separate pulls were conducted for the Control samples and 5 separatepulls were conducted for cables formulated using the Sample Iformulation. FIGS. 4-7 illustrate a comparison of the different requiredpulling forces for the Sample I and Control formulations tested in 500kcmil copper (FIGS. 4 and 5) and 750 kcmil aluminum (FIGS. 6 and 7)products. As illustrated in these figures, the Sample I formulation withthe aluminum conductor (FIGS. 6 and 7) resulted in a lesser averagepulling force than the standard XHHW product with the externally appliedindustry standard Y77.

In accordance with an advantage of the present invention, the pullinglubricant that is incorporated in the sheath is present at the outersurface of the sheath when the cable engages, or in response to thecable's engagement with, the duct or other structure through which thecable is to be pulled. For the cables of the present invention, wherethe outer sheath is of crosslinked polyethylene and the preferredpulling lubricant is polydimethylsiloxane, the lubricant permeates theentire crosslinked polyethylene sheath portion and is, in effect,continuously squeezed to the sheath surface in what is referred to asthe “sponge effect,” when the cable is pulled through the duct. Wherethe preferred lubricant is a fatty acid amide such as erucamide oroleamide, the lubricant migrates to the surface of the sheath.

Although the aforementioned description references specific embodimentsand processing techniques of the invention, it is to be understood thatthese are only illustrative. For example, although the description hasbeen with respect to electrical cable, it is also applicable to othertypes of non-electrical cable such as, for example, fiber optic cable.Additional modifications may be made to the described embodiments andtechniques without departing from the spirit and the scope of theinvention as defined solely by the appended claims.

That which is claimed:
 1. An electrical cable having a reducedinstallation pulling force through a building passageway, the electricalcable comprising: at least one conductor capable of carrying anelectrical current through the electrical cable, wherein the conductoris formed at least in part from a metal; and a sheath for protecting theconductor, wherein the sheath comprises a solidified extrusion of amaterial mixture, the material mixture comprising: a first polymericblend comprising a silane-ethylene copolymer resin and a pullinglubricant, wherein the silane-ethylene copolymer is provided as acarrier for the lubricant as a non-crosslinked resin, and wherein thepulling lubricant is a silicone material provided in an amount of atleast 25 wt % of the total weight of the first polymeric blend; a secondpolymeric blend comprising polyethylene; and a flame retardant; whereinat least some of the silane-ethylene copolymer resin is crosslinkedwithin the material mixture in the presence of a catalyst mixed with theflame retardant; and wherein the pulling lubricant is present in anamount greater than 2 wt % of the total weight of the material mixtureand at least a portion of the pulling lubricant is present at an outersurface of the sheath to reduce the pulling force necessary to pull theelectrical cable through the building passageway.
 2. The electricalcable of claim 1, wherein the material mixture further comprises asilane pre-grafted polyethylene and wherein at least some of the silanepre-grafted polyethylene is crosslinked.
 3. The electrical cable ofclaim 1, wherein the pulling lubricant is provided in an amount lessthan 15 wt % of the total weight of the material mixture.
 4. Theelectrical cable of claim 1, wherein the pulling lubricant ispolydimethylsiloxane.
 5. The electrical cable of claim 4, wherein thepulling lubricant is provided in an amount of less than 15 wt % of thetotal weight of the material mixture.
 6. The electrical cable of claim1, wherein the material mixture is homogeneously blended.
 7. Theelectrical cable of claim 1, wherein the first polymeric blend isprovided in a range of about 20 wt % to about 99 wt % based on the totalweight of the material mixture.
 8. The electrical cable of claim 1,wherein the sheath comprises a plurality of sheath layers, and at leastone of the sheath layers comprises the material mixture.
 9. Theelectrical cable of claim 8, wherein the sheath comprises an innersheath layer and an outer sheath layer, and wherein the outer sheathlayer comprises the material mixture.
 10. The electrical cable of claim1, wherein the sheath provides the electrical cable with the physicalcharacteristic of requiring at least 30% less force to pull theelectrical cable through the building passageway compared to an amountof force required to pull a non-lubricated electrical cable of the sametype and having an extruded sheath without the pulling lubricant mixedtherein through the building passageway.
 11. The electrical cable ofclaim 1, wherein the silane-ethylene copolymer resin is crosslinkable byexposure to moisture in the presence of a crosslinking catalyst.
 12. Theelectrical cable of claim 1, wherein the extruded sheath has a roundprofile.
 13. The electrical cable of claim 1, wherein the pullinglubricant is present in an amount greater than 3 wt % of the totalweight of the material mixture.
 14. The electrical cable of claim 13,wherein the pulling lubricant is present in an amount less than 15 wt %of the total weight of the material mixture.